Rotary flows are generated in a variety of technical installations, such as, for example, burners, particle separators, etc.
In these uses, the particular properties of the rotary flows generated and consequently those of the swirl generator itself play an essential part. Thus, for example in burner construction, a swirl is imparted to the combustion air, in order, on the one hand, to accelerate mixing between the fuel and air and, on the other hand, to utilize a possible return flow to improve the ignition conditions.
One question, among others relating to the design of the swirl generator, is to decide which flames with which properties are produced by the burner. It is therefore desirable, for control and optimization of the flame properties, to have available a swirl body of variable swirl intensity and swirl distribution.
In principle, swirl can be generated in several ways:
1. By means of a drive via rotating blades.
2. As a result of tangential introduction of the flow medium through a nozzle.
3. By means of guide blades in a radial channel and the result of subsequent deflection of the rotary flow in an axial direction.
4. By means of guide blades arranged axially.
A specific swirl distribution and category of flows are assigned to each of these swirl generators. In all cases, it is expensive in terms of construction to execute variable adjustment of the swirl intensity, which can be achieved by means of a controllable proportion with unswirled medium or by means of adjustable pitch angles of the guide blades. In burner construction, swirl generators with guide blades arranged axially are in widespread use, since a compact and simple design is guaranteed with these. However, precisely in the case of this type of swirl generator, measures for producing different swirl intensities are extremely difficult, with the result that a set of several swirl generators with different pitch angles of the guide blades is generally adopted.